308 THE DISEASES OF PLANTS. 



the plant, that is to say, the vessels which convey the jui- 

 ces, the leaves which elaborate them, the buds which pro- 

 duce flowers and fruit, are renewed every year ; they are 

 always fresh, always young : how then can a plant decay 

 from age ? 



Caroline. I should rather ask why all plants do not, 

 like annuals, die every year ? for these organs which are 

 renewed in the spring, perish in the autumn. 



Mrs. B. Of all the organs which are annually renewed 

 in perennial plants, the layer of wood and of bark alone 

 survive in an active state of vegetation : the others may 

 be considered as annuals, living but one season. 



Caroline. Then, when a tree dies of age, it is from 

 the stem being worn out : every year the wood hardens by 

 the pressure of the new layers which grow around it : its 

 vessels must, in consequence, become obstructed, and less 

 adapted to convey the fluids which are to pass through 

 them : this bears a strong analogy to the decay and death 

 of animals. 



Mrs. B. True ; but observe that if these vessels are 

 no longer calculated to transmit the juices, the plant no 

 longer requires them to execute this function : it is per- 

 formed by the fresh layer of wood and of bark which are 

 renewed every year : the old repose after their labors, but 

 do not perish ; age, therefore, does not necessarily entail 

 death, as in the animal kingdom. 



Emily. From what cause, then, do plants die ? for, 

 though some trees live to a great age, they all ultimately 

 perish, as well as animals. 



Mrs. B. They are certainly not destined to immortal- 

 ity ; but their ceasing to exist seems to depend upon some 

 accidental disease proving fatal, rather than upon any 

 prescribed term of years assigned to them by Nature. 



The malady which most commonly destroys plants is 

 exhaustion, arising from their bearing, and ripening, too 

 great a number of seeds : it is this which regularly, though 

 not necessarily, occasions the death of annuals; for, if from 

 any accidental circumstance the seeds are not matured, the 

 plant retains sufficient vigor to live through another season. 



1663. Caroline asks, why all plants do not die every year What is 

 the answer 1 1664. What does Caroline suppose when a tree dies 

 from age*? 1665. What additional remarks does Mrs. B. make upon 

 what Caroline says! 1666. Emily asks From what cause plants do 

 die What is the answer of Mrs. B.I 1667. With what malady do 

 they most commonly die! 



